Described below is a method and a device for separating a magnetically guided endoscopy capsule from a water surface with the aim of immersing the capsule completely in water and thereby separating the capsule from the water surface, using the least possible magnetic force.
The use of endoscopy capsules is increasingly widely applied in medicine for diagnosing or treating the inside of a patient. An endoscopy capsule may contain, amongst other things, medical instruments, for example for carrying out a biopsy or for introducing medication into the body, and/or imaging systems such as cameras. The endoscopy capsule has a magnetic element which is fixedly connected to the capsule and includes a magnetic dipole moment which may originate, for example, from a permanent magnet fixedly installed in the capsule. Due to the magnetic dipole moment the capsule may be maneuvered and/or navigated in any manner by a maneuvering device, as disclosed, for example, in DE 10 2008 004 871.
DE 10 2008 004 871 discloses a solenoid system consisting of a plurality of individual coils for navigating an endoscopy capsule, a video capsule or any other probe. Hereinafter simply an “endoscopy capsule” is generally referred to, or in brief a “capsule”, the endoscopy capsule, the video capsule and the other probes being incorporated within this term. A magnetic element, for example a permanent magnet or ferromagnet, is fixedly installed in the capsule so that it may be maneuvered in any manner by the solenoid system. The solenoid system generates magnetic field components Bx, By, Bz along the x, y, z axes of a Cartesian coordinate system and magnetic gradient fields which permit contactless guidance of the endoscopy capsule.
In this case—in the absence of significant mechanical counter forces—use is made of the fact that the magnetic element, i.e. a body with a magnetic dipole moment {right arrow over (m)}, is oriented parallel to the direction of the magnetic field {right arrow over (B)}, formed by the magnetic field components BX, By, Bz in the direction of the axes of the Cartesian coordinate system. As the magnetic element is fixedly connected to the endoscopy capsule, the orientation of the capsule may be influenced in this manner. Additionally, triggered by the magnetic gradient fields ∂Bx/∂x etc. a force {right arrow over (F)}=G·{right arrow over (m)} acts on the magnetic dipole moment {right arrow over (m)} with a gradient matrix G comprising the gradient fields according to
      F    →    =                    G                  _          _                    ·              m        →              =                  (                                                                              ∂                                      B                    x                                                                    ∂                  x                                                                                                      ∂                                      B                    x                                                                    ∂                  y                                                                                                      ∂                                      B                    x                                                                    ∂                  z                                                                                                                          ∂                                      B                    y                                                                    ∂                  x                                                                                                      ∂                                      B                    y                                                                    ∂                  y                                                                                                      ∂                                      B                    y                                                                    ∂                  z                                                                                                                          ∂                                      B                    z                                                                    ∂                  x                                                                                                      ∂                                      B                    z                                                                    ∂                  y                                                                                                      ∂                                      B                    z                                                                    ∂                  z                                                                    )            ·              m        →            
The gradient matrix G is symmetrical and trace-free due to the Maxwell equations rot {right arrow over (B)}=0 and div {right arrow over (B)}=0, i.e. it contains with ∂Bx/∂y (=∂By/∂x), ∂Bx/∂z (=∂Bz/∂x), ∂By/∂z (=∂Bz/∂y) and two of the three diagonal elements (for example ∂Bx/∂x and ∂By/∂y) five independent gradient fields.
The magnetic field {right arrow over (B)} and one or more of the gradient fields of the matrix G may be set in any manner via a targeted activation of the individual coils of the solenoid arrangement. It is, therefore, possible firstly to rotate the magnetic element and/or the capsule and thus to align the magnetic element and/or the capsule in any manner in a work space A within the solenoid system. Secondly, it is possible to exert a force {right arrow over (F)} on the magnetic element in order to shift it translationally in addition to the rotation.
For a more detailed explanation of the navigation of the capsule by the various fields generated by the solenoid system, reference is made in particular to DE 10 2008 004 871.
A specific application of magnetic capsule endoscopy is so-called stomach screening which involves an examination of the stomach and is disclosed, for example, in US 2007/0221233 A1. In stomach screening, the stomach is partially filled with water and the capsule and/or a camera integrated into the capsule is intended to take long-distance and close-up images of the stomach lining, the optical axis of the camera generally being oriented in the direction of the longitudinal axis of the capsule and generally being fitted into the capsule at one of the capsule ends. With long-distance images, the capsule generally floats on the water surface, one of the two generally semi-spherical capsule ends partially protruding from the water surface. For close-up images, the capsule is typically completely immersed in water. For the transition from long-distance images to close-up images, the capsule consequently has to be separated from the water surface, for which a magnetic force has to be applied to the capsule in the order of approximately 2 mN due to the surface tension of the water. This separation force is markedly greater than the magnetic force which is required to move the capsule slowly, i.e. in the case of stomach screening at a speed of 0-5 mm/sec, either in two dimensions on the water surface or three-dimensionally, completely immersed in the water. Typically, forces are required here in the order of approximately 0.2 mN to 0.3 mN, this only being applicable with a vertical movement of a capsule completely immersed in water, when the average density of the capsule is approximately the same as the density of water.
The exerted magnetic force is proportional to the coil currents in the individual coils of the solenoid system. In order to generate the magnetic force on the capsule required for complete immersion, accordingly coil currents and/or a number of ampere turns are required in the magnetic coils which markedly exceed the currents and/or number of ampere turns required for normal navigation of the capsule. Accordingly, expensive power amplifiers which can generate the higher currents are required and correspondingly more efficient cooling systems.
One possibility for reducing the influence of the surface tension is to pivot the capsule floating on the water surface such that the end protruding from the water surface is wetted with water. After wetting, the capsule behaves as a completely immersed capsule which floats just below the water surface, i.e. a specific separation force is no longer required for lowering the capsule. When pivoted, however, inevitably the viewing angle of the capsule and/or of the area reproduced by the camera is altered. Accordingly, the target area of the stomach lining which is to be observed more closely and which, for example, has been identified by the long-distance images, generally moves out of the field of view of the camera when pivoted. The target area then has to be found again before it is possible to continue with the more detailed examination which with the relatively low image refresh rate of the capsule camera and under the optical conditions in the stomach may be very time-consuming.